DYNAMIC CAPILLAROSCOPY - A MINIMALLY INVASIVE TECHNIQUE FOR ASSESSINGPHOTODYNAMIC EFFECTS IN-VIVO

A noninvasive method for visualizing the microvasculature in the mouse tail is described, consisting of a custom-built microscope with throu gh-lens illumination. The microscope is fitted with a television camer a and images can be recorded on videotape and displayed on a televisio n monitor. Blood vessels are imaged as columns of red blood cells, in which flow is clearly observed. Administration of photosensitizers and illumination with the standard light source produces no observable ph otodynamic effect on blood flow. The combination of photosensitizer an d a more intense light source (either broadband light from a filtered mercury are or red light from a laser) causes photodynamic cessation o f flow within a few minutes. The magnitude of the effect is dependent on the dose and nature of the photosensitizer, the delay after photose nsitization and the match between the laser light and the absorption s pectra of the photosensitizers in the red region. We conclude that the technique yields results consistent with the known photodynamic effec ts of the photosensitizers in tumors and propose its use as an initial screening method in vivo, as a means of conducting pharmacokinetic ex periments and as an assay of prolonged cutaneous photosensitivity.